Inertia Friction Welding Research Articles

The Coupled Thermal Mechanical Modeling of the Inertia Friction Welding Process for Inconel718

In this paper, numerical modeling of inertia friction welding (IFW) for Inconel718 was performed using ABAQUS/Explicit with a 3D finite-element (FE) model and the coupled thermo-mechanical analysis. A new thermal input model has been deduced according to the characteristics of IFW and law of conservation of energy. The evolution of temperature field as well as the deformation pattern of the inertia welded joint has been predicted. It is shown that the interface temperature firstly increases rapidly to about 1100 °C within 3 s and then increases slowly. The energy input rate at the interface during the IFW process is closely related to the rotational speed and friction torque of flywheels. The temperature distribution at the interface is very inhomogeneous especially at the initial stage and finally tends to become uniform with the increase of time. Consequently, the flash start to appear as the interface temperature becomes homogeneous relatively and the plastic flow of metal at the interface happens. The verifying trial was carried out and the predicted temperature was compared with the experimental data measured by means of thermocouples. The shape of flash in simulation result was contrasted with the true shape of specimen under the same welding conditions. It is noted that the simulation results agrees well with the experimental results.

Radial friction welding interface between brass and high carbon steel

CT-130 special inertia friction welding machine is used to finish a large size (156 mm diameter) of H90 brass/D60 steel dissimilar welding. SEM, EDS methods are used to analyze the interfacial characteristics of H90/D60 welding joint. The results show that in the welding interface, some furrow-shaped holes appear at the end of welding joint, and a smooth line occurs in the central welding interface and a good welding seam is formed. Thermoplastic brass is droved and flowed to the edge of welding interface under radial pressure, which becomes a lubricating thin film, and reduces the friction coefficient of welding joint edge, leads to that phenomenon. It is found that Fe and Cu elements diffusion appeared at the welding interface. But the density and distance of Fe element diffusion towards H90 brass are larger than that of Cu element towards D60 steel, which is attributed to the difference of the lattice coordination number of Fe/Cu.

A Comparison of Residual Stress Development in Inertia Friction Welded Fine Grain and Coarse Grain Nickel-Base Superalloy

The effect of the base material microstructure on the development of residual stresses across the weld line in inertia friction welds (IFWs) of high-strength nickel-base superalloy RR1000 was studied using neutron diffraction. A comparison was carried out between tubular IFW specimens generated from RR1000 heat treated below (fine grain (FG) structure) and above (coarse grain (CG) structure) the γ′-solvus. Residual stresses were mapped in the as-welded (AW) condition and, after a postweld heat treatment (PWHT), optimized for maximum alloy strength. The highest tensile stresses were generally found in the hoop direction at the weld line near the inner diameter of the tubular-shaped specimens. A comparison between the residual stresses generated in FG and CG RR1000 suggests that the starting microstructure has little influence on the maximum residual stresses generated in the weld even though different levels of energy must be input to achieve a successful weld in each case. The residual stresses in the postweld heat treated samples were about 35 pct less than for the AW condition. Despite the fact that the high-temperature properties of the two parent microstructures are different, no significant differences in terms of stress relief were found between the FG and CG RR1000 IFWs. Since the actual weld microstructures of FG and CG RR1000 inertia welds are very similar, the results suggest that it is the weld microstructure and its associated high-temperature properties rather than the parent material that affects the overall weld stress distribution and its subsequent stress relief.

Detailed Diffraction and Electron Microscopy Study of Inertia-Friction-Welded Dissimilar High-Strength Steels

A detailed characterization of two dissimilar high-strength steels, SCMV and Aermet 100, joined by inertia friction welding (IFW)—a solid-state welding technique—was undertaken using high energy synchrotron X-ray diffraction and advanced electron microscopy in order to understand the dramatic hardness variation across such a weld. It was found that the severe high-temperature deformation in the thermomechanically affected zones (TMAZs) of the weld, stabilized ordered, and nanosized FeCo zones in Aermet 100 and about 12 to 14 vol pct austenite in SCMV (Ni equivalent 9 wt pct). The ordered FeCo zones in Aermet 100 resulted in exceptionally high hardness values of 700 to 725 HV. Very close to the weld line, the TMAZ of Aermet 100 also displayed a region with about 15 vol pct austenite, while in the parent material, 8 to 9 vol pct was typically observed. No indication of martensite was found in the weld region of Aermet 100. Ferrite texture analysis at different locations within the TMAZs on either side of the weld showed that SCMV develops a very strong α-fiber texture near the weld line and, in addition, a γ-fiber texture toward the heat-affected zone (HAZ), suggesting the presence of ferrite during welding near the weld line and recrystallization further away. The ferrite texture development in the TMAZ of Aermet 100 was relatively weak, suggesting that austenite is a dominant phase in the TMAZ during IFW.

Characterization of the Weld Line Zones of an Inertia Friction Welded Superalloy

The Inertia Friction Welding (IFW) process is a high-temperature and high pressure process, with heavy plastic deformation, high power density, fast heating and fast cooling of the weld material. The microstructure produced in the weld line （WL）zones is therefore very different from parent material. A detailed microstructural investigation of the WL zones has been conducted using transmission electron microscopy and scanning electron microscopy. It has been shown that the morphology, energy status and microchemistry of grain boundaries in the WL zones are quite different from those in the parent material. It is also observed that, compared to a bi-modal distribution of intragranular ¢ particles in the parent material, a unimodal distribution of very fine spherical ¢ particles is produced in high density in the WL zones. This work provides a detailed understanding of the physical and chemical changes occurring across the weld line.

Electron microscopy characterization of the weld line zones of an inertia friction welded superalloy

Microstructure in the weld line (WL) zone produced by inertial friction welding has been studied for a series of RR1000–RR1000 welds using transmission electron and scanning electron microscopy. A fully recrystallised fine grain structure was found to form throughout the WL zone, characterized by straight and smooth grain boundaries, high energy status and modified grain boundary chemistry due to very fast cooling after welding. Very fine γ′ particles with unimodal size distribution were reprecipitated in the WL zone. The fine γ′ particles are spherical in shape, high in number density and characterized by an imbalanced chemistry, containing less Al, Ti, Ni, Ta γ′-forming elements but more Cr, Co, Mo γ-forming elements than all types of parent γ′ particles. As a result, a hard and strong WL zone was produced by the inertial friction welding.

Effect of rotation speed on temperature field and axial shortening of inertia friction welded GH4169 joints by numerical simulation

A 2D finite element model was established for inertia friction welding of GH4169 nickel-base superalloy based on the ABAQUS environment. The remeshing and map solution techniques were adopted to solve the problem of element distortion. The effect of rotation speed on the temperature field and axial shortening of joints was investigated. The results show that the interface temperature increases rapidly to higher than 900°C within 1 s. And then, it increases slowly to a quasi-stable value. The axial shortening begins to augment quickly when a uniform interface temperature field has formed and the plasticized material is extruded from the interface to form an obvious flash. The rotation speed of the flywheel controls the welding process and has a significant influence on the temperature evolution and axial shortening of joints.

A transient finite element analysis of thermoelastic effects during inertia friction welding

A fully coupled torsional elastic–plastic finite element model has been used to assess the thermoelastic effects (thermal expansion) during the inertia friction welding process of the nickel–chromium alloy, Inconel 718. The two workpieces are initially in conforming contact and the generation of heat causes local thermal expansion which results in a non-uniform pressure distribution across the contact area and a reduction in the contact area between the workpieces. Eventually the material around the weld interface heats up sufficiently for the axial load to cause plastic flow to occur which results in an increase in the contact area. The effect of the axial pressure and sliding velocity on the minimum contact area and the time taken to recover 90% of the initial contact area is investigated using the finite element model.

Experimental and Numerical Thermomechanical Analysis of Hybrid Friction Welding of Commercially Pure Copper Bars

Friction welding is a solid-state welding process accomplished by direct conversion of mechanical energy into the thermal energy at the interface of workpieces without melting. The friction welding process can be controlled through different parameters, such as angular velocity, pressure, temperature, stress and strain distribution, and so on. The welding machine design as well as welded part quality could be significantly improved by understanding and optimizing the process parameters. Hybrid friction welding (HFW) is introduced as one of the rotary friction welding processes that benefits advantages of continuous drive friction welding and inertia friction welding, while attempts have been made to eliminate the disadvantages of old friction welding processes. In this study, three-dimensional thermomechanical simulation of hybrid rotary friction welding of equal diameter copper workpieces has been carried out and the effect of various parameters, especially the pressure, on the thermomechanical behavior and the shape of welded zone has been investigated.

Finite Element Simulation of Microstructural Evolution during Inertia Friction Welding Process of Superalloy GH4169

During the inertia friction welding (IFW) process of superalloy GH4169, the main mechanism for microstructural evolution is dynamic recrystallization (DRX). In order to investigate the microstructural evolution during the process, a finite element (FE) model coupled with the DRX model of the alloy was developed on the platform of MSC.Marc. Equivalent strain was introduced into the DRX model to improve the computational precision. As a result, the IFW process with microstructural evolution was simulated. Simulated results reveal that DRX region is very small. Fully recrystallized region and fine grains appear near the weld line. Dynamically recrystallized fraction (DRXF) decreases and grain size increases with the increase of the distance from the weld line. Predicted results of microstructural distribution agree well with experimental ones.

Thermal Relaxation of Residual Stresses in Nickel-Based Superalloy Inertia Friction Welds

This article describes an experimental study aimed at characterizing the extent of residual stress relaxation during thermal treatment of inertia friction-welded alloy 720Li nickel-based superalloy welded tubular rings. In the as-welded condition, yield level tensile hoop stresses were found by neutron diffraction in the weld region along with axial bending stresses (tensile toward the inner diameter (ID)/compressive toward the outer). The evolution of these residual stress levels during postweld heat treatment (PWHT) was mapped experimentally over the weld cross section. After 8 hours of PWHT, the axial stresses relaxed by 70 pct, whereas the hoop stresses reduced by only 50 pct. Some scatter of residual stress evolution was found between samples, particularly for the axial stress direction. This was attributed to substandard tooling to grip the rings. The results on subscale samples were transferred to a full-scale aeroengine (650-mm diameter) compressor drum assembly that was postweld heat treated for 8 hours. It was found that the residual stresses, particularly in the axial direction, were noticeably lower in this full-scale weld component compared to the subscale weld heat treated for the same time. The differences seem to be best rationalized by the different standards of jigging used during joining these two types of welds.

Distribution and Variation Characteristics of Temperature in Inertia Friction Welded Inconel 718 Joint

The temperature evolution in inertia friction welded Inconel 718 joint was measured by means of embedding thermocouples in specimens. The spatial distributions of temperature in the axial and radial directions of weldments were obtained and the varying characteristics of the temperature distributions were analyzed. The results indicate that the heating rate during the inertia welding process decreases gradually. The temperature distribution in the radial direction of weldment is uneven and the temperature rises gradually with the increase of distance from the center. But the relation between the temperature and distance is nonlinear. In the axial direction, the shorter the distance from the initial friction surface is, the bigger the rate of temperature increment becomes and the higher the peak temperature and the temperature gradient are. Meanwhile, the longer the distance from the initial friction surface is, the later the peak temperature appears and the longer the delay time gets. Moreover, the results of microhardness testing in a welded joint prove that the measurement of temperature in this study is reliable.

Fatigue Crack Propagation Behavior of an Inertia Friction Welded α/β Titanium Alloy

Abstract The inertia friction welding process is being extensively investigated for the joining of high strength titanium alloys for aerospace applications. Although it offers solid state joining, the thermal cycle and deformation involved results in microstructural inhomogeneity across the weld interface. In this paper, the fatigue crack propagation behavior in an inertia welded microstructure in a high strength, high temperature α/β titanium alloy is considered. The fatigue crack propagation behavior in corner notched weld specimens at varying stress ratios is studied at room and elevated temperatures and compared with that of the parent material. Fatigue crack growth rates at lower stress intensity ranges are comparable with those in the parent material. However, in weld specimens tested at room temperature, unstable crack growth occurs at lower stress intensity range values compared to that at high temperature. Fracture surface observations show that this difference is related to a change in fracture mode from transgranular to intergranular/mixed mode during room temperature tests. This change in fatigue crack growth mechanism is deduced to be due to low ductility intergranular failure of grain boundary α in the refined transformed beta microstructure across the weld interface.

Inertia friction welding process analysis and mechanical properties evaluation of large rotor shaft in marine turbo charger

The two aims of this study are first, determining the optimal welding process parameters by using the finite element simulation and second, determining the optimal tempering temperature by evaluating the mechanical properties of friction welded part for manufacturing large rotor shaft. Inertia welding was conducted in order to make the large rotor shaft of turbo charger for low speed marine diesel engine. The rotor shaft is composed of the 310mm diameter disk and the 140mm diameter shaft. Since diameters of disk and shaft are very different, the integration using friction welding reduces manufacturing cost compared with the forming process of which a disk and shaft are forged into one body. Finite element simulation was performed, because inertial welding friction process depended on many process parameters, including axial force, initial revolution speed and energy, amount of upset, and working time. It is expected that this modeling will significantly reduce the number of experimental trials needed when determining the optimal welding parameters. Inertia welding was carried out with optimal process parameter conditions obtained from the simulation results. Welded joint part, made by friction welding, had very poor mechanical properties, and so it required heat treatment. The base material used in the investigation was SFCMV1 (SANYO special steel, high strength low alloy Cr-Mo steel) of 140mm diameter. In the study, heat treatment test carried out quenching (950 °C, 4hr, oil cooling) and tempering (690–720 °C, 6hr, air cooling) for friction welding specimens. The various tests, including microstructure observation, tensile, hardness, and fatigue tests, were conducted to evaluate the mechanical properties under various heat treatment conditions after inertia welding.

Microstructure and Property of Ni76Cr19AlTi Side in Inertia Friction Weld Joint of the Superalloy Ni76Cr19AlTi and the Martensite Stainless Steel 4Cr10Si2Mo

The inertia friction welding process was used to weld the nickel base superalloy Ni76Cr19AlTi to martensite steel 4Cr10Si2Mo. Ni76Cr19AlTi is a f.c.c superalloy strenthened by precipitates of γ′. 4Cr10Si2Mo is a martensite stainless steel strenthened by martensite transformation and precipitates of carbides. The microstructure evolution on the nickel base superalloy Ni76Cr19AlTi side of the weld was studied. It was found that the welds formed can be divided into three zones: thermomechanically affected zone, heat affected zone and base metal. The thermomechanically affected zone consisted of two subzones: one is the mixed chemical composition zone of about 100 μm in width formed by mechanical stirring and interdiffusion of alloying elements and the other was pure shear zone located adjacent to the mixedchemical composition zone. In the chemical composition mixture zone, a large number of carbides with sizes of less than 100 nm formed in the austenite matrix. However, no γ′ phase can be observed in this region. The dislocation density decreased gradually as the distance to the weld interface increased. The dislocation density in the pure shear zone was very high. Grain size coarsened markedly in the heat affected zone, in which the γ′ phase was precipitated. The primary mechanism of the grain growth was the bulging of grain boundary between two adjacent grains with high-angle boundary.

Dissimilar friction welding of 6061-T6 aluminum and AISI 1018 steel: Properties and microstructural characterization

Joining of dissimilar materials is of increasing interest for a wide range of industrial applications. The automotive industry, in particular, views dissimilar materials joining as a gateway for the implementation of lightweight materials. Specifically, the introduction of aluminum alloy parts into a steel car body requires the development of reliable, efficient and economic joining processes. Since aluminum and steel demonstrate different physical, mechanical and metallurgical properties, identification of proper welding processes and practices can be problematic. In this work, inertia friction welding has been used to create joints between a 6061-T6 aluminum alloy and a AISI 1018 steel using various parameters. The joints were evaluated by mechanical testing and metallurgical analysis. Microstructural analyses were done using metallography, microhardness testing, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray elemental mapping, focused ion beam (FIB) with ultra high resolution SEM and transmission electron microscopy (TEM) in TEM and STEM modes. Results of these analysis first suggested that joint strengths on the order of 250 MPa could be achieved. In addition, failures were seen in the plasticized layer on the aluminum side of the joint. Further, bond lines were characterized by a thin layer of formed Al–Fe intermetallic. This intermetallic layer averaged roughly 250 nm thick and compositionally appears related to the FeAl and Fe 2Al 5 phases.

Residual Stresses in Inertia-Friction-Welded Dissimilar High-Strength Steels

The welding of dissimilar alloys is seen increasingly as a way forward to improve efficiencies in modern aeroengines, because it allows one to tailor varying material property demands across a component. Dissimilar inertia friction welding (IFW) of two high-strength steels, Aermet 100 and S/CMV, has been identified as a possible joint for rotating gas turbine components and the resulting welds are investigated in this article. In order to understand the impact of the welding process and predict the life expectancy of such structures, a detailed understanding of the residual stress fields present in the welded component is needed. By combining energy-dispersive synchrotron X-ray diffraction (EDSXRD) and neutron diffraction, it has been possible to map the variations in lattice spacing of the ferritic phase on both sides of two tubular Aermet 100-S/CMV inertia friction welds (as-welded and postweld heat-treated condition) with a wall thickness of 37 mm. Laboratory-based XRD measurements were required to take into account the variation in the strain-free d-spacing across the weld region. It was found that, in the heat-affected zone (HAZ) slightly away from the weld line, residual stress fields showed tensile stresses increasing most dramatically in the hoop direction toward the weld line. Closer to the weld line, in the plastically affected zone, a sharp drop in the residual stresses was observed on both sides, although more dramatically in the S/CMV. In addition to residual stress mapping, synchrotron XRD measurements were carried out to map microstructural changes in thin slices cut from the welds. By studying the diffraction peak asymmetry of the 200-α diffraction peak, it was possible to demonstrate that a martensitic phase transformation in the S/CMV is responsible for the significant stress reduction close to the weld line. The postweld heat treatment (PWHT) chosen to avoid any overaging of the Aermet 100 and to temper the S/CMV martensite resulted in little stress relief on the S/CMV side of the weld.

CURRENT CAPABILITIES OF THE THERMO-MECHANICAL MODELLING OF WELDING PROCESSES

Some fundamental principles and advanced applications of thermo-mechanical modelling techniques used for industrial welding processes are described. The paper covers a range of modelling procedures comprising welding simulation and residual stress analysis of multi-pass, thick-walled ferritic steel pipes; welding simulation and distortion analysis of nickel-based superalloy thin plates; and inertia friction welding of dual alloy drive shafts. A number of pertinent mechanical and metallurgical concepts are discussed, including material behaviour models and material properties, microstructural evolution, solid state phase transformation and post-weld heat treatment. The paper emphasises the general methodologies of thermal modelling procedures and their role in the holistic process of the life assessment and design improvement of power plant piping systems and aeroengine casings and shaft components, operating under high temperature creep and fatigue service conditions.

Sequential Transient Numerical Simulation of Inertia Friction Welding Process

Inertia friction welding processes often generate substantial residual stresses due to the heterogeneous temperature distribution during the welding process. The residual stresses, which are the results of incompatible elastic and plastic deformations in weldment, will alter the performance of welded structures. In this study, three-dimensional (3D) finite element analysis has been performed to analyze the coupled thermo-mechanical problem of inertia friction welding of a hollow 36CrNiMo4 cylinder. The analyses include the effect of conduction and convection heat transfer in conjunction with the angular velocity and the thrust pressure. The results include joint deformation and a full-field view of the residual stress field and the transient temperature distribution field in the weldment. The shape of deformation matches the experimental results reported in the literature. The residual stresses in the heat-affected zone have a high magnitude but comparatively are smaller than the yield strength of the material.

Finite element process modelling of inertia friction welding advanced nickel-based superalloy

A sequentially coupled thermal and mechanical finite element (FE) model has been developed to describe inertia friction welding (IFW) using the DEFORM 8.2 package. All modelling and experimental work was undertaken on inertia friction welds made from RR1000, which is an advanced high γ′ content nickel-based superalloy. The accuracy of the thermal predictions has been assessed by an analysis of γ′ distribution across the weld region as compared to those recorded during prescribed thermal simulations, while the mechanical model has been validated by comparing predicted and measured upsets and weld pressures. Finally the residual stress predictions have been compared against measurements (by neutron diffraction). In all cases excellent agreement was found between predicted and experimental data. This exercise revealed that the clamping forces applied during the welding process may have a strong influence on the axial stress field. The validated model was then used to study the effect of welding pressure on material flow, thermal history and residual stresses. The work shows that with increasing weld pressure the width of the heat-affected zone (HAZ) is reduced, while the peak temperature and strain rate is increased. In addition the peak stresses in the hoop direction near the weldline were found to be largely unaffected by the weld pressure. However, for lower welding pressures a broader high tensile hoop stress region was found in accordance with the increased HAZ.